Ok here goes the tale. I recently noticed that my 1996 Audi A4 110bhp TDI was loosing coolant fluid. On inspeciton I foudn that it seemed to be boiling off at the top hose to the radiator was too hot to touch, but the radiator was cold. Having searched the net I replaced the expansion cap as a starting point but no change. These weekend I replaced the thermostat and things have changed a little. Instead of the temperature gauge sticking like glue to 90degrees it now goes up when I accelerate hard but then after a while returns to 90. The radiator is hot across the top and this morning after a 60 mile run was warm in other places too. With the engine hot and running I have tried to hold shut the top line to the radiator after the T to the expansion tank in the hope of seeing water
puped into tank to confirm water pump is working but to no avail. Should I go ahead and replace water pump of does anyone else have any bright ideas, for reference the system seems to hold pressure once the car has cooled down as when I open expansion tank it goes psss and level rises in tank, plus oil is black with no milky streaks.

Any ideas would be well and truly welcome.

Thanks

Andrew

PS Does anyone also know how to stop water accumulating in batery tray?

OK run engine until Hot, Slowly and carefully releast the pressure to zero, do up the cap and drive another few miles quite hard. Now recheck water pressure in system. If this has re-flated then I am afraid you may have a minot combustion chamber to warerway leak, thus no water in oil, and if minor you only leach a lillte water into the piston. Check the plugs to see if you hace a jet washed one which would imply a larger leak but have had several of these with only minor leaks. The tiny stream of bubbles in the water also caused air locks and local overheating if pushed. A good diagnosic garage can sniff the header tank vapours for exhaust fumes. These type of leaks get worse and can errode a track into the Ali head. No you can not use radweld or whatever as the air flow is in the wrong direction. Regards Peter

Ps the excess pressurisation cuased considerable reduction of the water level in the header and on releasing the presssure can then indicate and overfilled tank you to the bubbles trapped in the system. Do not forget that the cap vents off excess pressure may be a 1 to 1.4 bar and on cooling allows air into the system to stop the hoses form collasping. Regards Peter

I don't know about your coolant loss, but I have some advice about the water in the battery tray. I did have the same problem on my A4 and have it also on my current car, a Passat 110 TDi.

There is a drain hole in the battery tray which blocks easily, but of course it is hidden right under the battery and you need to remove the battery to clean it. Remove the wipers (mark their position on the screen to aid refitting) and the black plastic trim from the bottom of the screen. Then disconnect and unbolt the battery to remove it. Remember that if removing the battery, you need the code for the radio to reactivate it once power is restored. Also be aware that there are reports of failure of the MAF (the Mass Air Flow sensor) on disconnection of the battery. It might be prudent to find some way of keeping the power on whilst moving the battery.